Traditional braking such as drum or disc braking systems have been widely used in a range of vehicle applications. However, brake fade caused when the drums or discs and the linings of the brakes overheat from excessive use become particularly problematic in large vehicle applications. Traditional braking systems usually require regular maintenance to service and replace consumable components, such as brake pads. Large vehicles such as locomotives, semi-trailer trucks, waste collection vehicles, construction vehicles and other large multi-axle vehicles require considerable braking power to adequately control braking, particularly when the vehicle is carrying a load. Reliability of braking systems can have significant implications in terms of safety and cost.
As an alternative to traditional friction resistance brakes, liquid resistance or direct hydraulic braking have been used which do not rely on friction to transmit braking force. However, these systems have been limited in application due to sizes required to achieve the desired braking efficiency and modulation capability. The use of a hydraulic pump in direct hydraulic braking, having a reciprocating piston, can require significant fluid displacement to achieve desired brake horse power (BHP). However, the relatively large displacement required to achieve high braking can impact the design of piston units, for example requiring larger sized units due to larger bores and/or increased stroke lengths, thus limiting their application.